Mass spectrometer and electrically conductive display member therefor



MASS SPECTROMETER AND ELECTRICALLY CONDUCTIVE DISPLAY MEMBER THEREFOR Filed Aug. 23, 1967 y 1970 'r. H. BRIGGS EITAL 3,510,646

INVENTORS x H. BRIGGS 1. R PR/CHETT A TTORNEV United States Patent 3,510,646 MASS SPECTROMETER AND ELECTRICALLY CONDUCTIVE DISPLAY MEMBER THEREFOR Thomas H. Briggs, Allentown, and Peter P. Prichett,

Bethlehem, Pa., assignors to Western Electric Company, Incorporated, New York, N.Y., a corporation of New York Filed Aug. 23, 1967, Ser. No. 662,787 Int. Cl. G03b 29/00 U.S. Cl. 250-413 3 Claims ABSTRACT OF THE DISCLOSURE An improved display member for a mass spectrometer of the type wherein a beam of ions is projected from an ion source into a mass analyzer having a display member, such as a transparent substrate coated with photosensitive material. The improved display member includes a substrate, an electrically conductive film on the sub strate and a coating of material sensitive to ions deposited on the substrate, whereby the display member is provided with electrically conductive characteristics to reduce spurious indications, such as fogging, caused by reflected ions and other electrically active emissions.

BACKGROUND OF THE INVENTION This invention relates to improved mass spectrometers and display members therefor and in particular to electrically conductive display members for mass spectrometers. Accordingly, the general objects of the invention are to provide new and improved apparatus of such nature.

A mass spectrometer is commonly used as an appara tus for analyzing the constituent elements of a material. The material is ionized in a part of the apparatus which may be termed the ion source, and a beam of ions of the material is projected from the ion source into the mass analyzer, The ions are formed from the constituent elements of the material and since these elements have different positions in the periodic table, the masses of the ions will generally be different.

A description of mass spectrometry together with apparatus which can be modified in accordance with this invention is set forth in US. Pat. 2,993,992 to R. D. Craig, issued July 25, 1961, which suggests that ions can be deflected by a magnetic field onto a photographic plate or film.

The mass spectrometers described in the aforesaid Craig patent can be modified by electrostatic focusing means as taught by R. D. Craig in US. Pat. 3,217,-

161, issued Nov. 9, 1965.

Mass spectrometers are described in US. Pat. 2,642,- 535 to A. C. Schroeder, issued June 16, 1953, Schroeder sets forth the operation of mass spectrometry and describes various techniques for accelerating, decelerating, and focusing a beam of ions. Mass spectrometers are described utilizing fluorescent screens and ion multipliers.

Mass spectra can be recorded on photoplates so that a continuous range of mass numbers are integrated simultaneously from an irregular discharge. The photoplates can consist of a thin layer of a silver halide-gelatin 3,510,646 Patented May 5, 1970 mixture on a glass substrate. An image is obtained by allowing accelerated ions to impinge on the plate in a series of lines according to the masses of the isotopes comprising the beam. The plate is developed as any other photographic material would be.

It has been the practice, in the prior art, to use a transparent film or glass substrate having a photographic emulsion thereon in combination with the mass spectrometer. However, results were limited because, when positive ions strike the emulsion, they produce not only a mass line spectrum, but also soft X-rays, luminescence, negative ions, secondary electrons, and reflected positive ions, all of which fog the emulsion which degrades the resultant image, The fogging is appreciable when the integrated ion charge is suflicient to record an element at onepait-per-billion atomic fraction. The subsequent loss in detection sensitivity is greatest in the general vicinity of the major component.

With such a mass spectrograph, the fogging can be partially suppressed by placing a grounded metallic strip over that section of the emulsion struck by the ions of the major component, as taught by N. B. Hannay, Review of Scientific Instruments, vol. 25, pages 644 to 648 (1954). The problem of fogging was recognized by A. J. Ahearn and D. L Malm in an article, Background Reduction in Photographs of Mass Spectra in Applied Spectroscopy, pages 411 and 412, vol. 20, No. 6, 1966. Ahearn et a1. teach the removal of that segment of the photographic plate Where the major component normally strikes and replacing it with a Faraday cage to trap those ions as well as their secondary products.

Both Hannay and Ahearn et al. require the identification of the major component of the material being analyzed prior to the modification of their equipment.

Long exposure spectra have extremely heavy background, broadened lines, and streamers originating from the. most intense lines. These effects are undesirable in that they impair sensitivity of ion detection and the ability to resolve weaker lines in the vicinity of the intense lines.

These impairments are caused by several phenomena. One major one is that the impingement of the ion beam creates an appreciable surface charge of the same polarity as the incoming beam.

Since the photosensitive emulsion and glass are both insulators, the charge decays slowly, often requiring more than 30 minutes. Another cause of background is that secondary electrons and ions are evolved, but with less energy than the primary beam. In the magnetic field of the mass spectrograph, these particles return to the plate and create a background.

Electrically conductive display members per se have existed in the prior art. For example, the aluminized picture tube used in a television receiver includes a glass face plate having cathodoluminescent phosphors deposited thereon and a thin layer of aluminum coated onto the phosphors. The aluminum coating functions primarily to increase the amount of light being transmitted to the viewer due to its reflective characteristic. Other electrically conductive display members are suggested in the prior art such as Dalton et al. US. Pat. 2,983,221, issued May 9, 1961, entitled Planographic Printing Plates. Also, electrically conductive photographic or motion picture film are suggested in US. Pat. 1,471,592 to Coberly, issued 3 Oct. 23, 1923; US. Pat. 1,570,078 to Pitman, issued Jan. 19, 1926; and US. Pat. 1,687,041 to Seel, issued Oct. 9, 1928. Coberly describes the combination of a conducting 4 layer on to a transparent supporting material together with the sensitized emulsion thereon in order to render the photographic film nonstatic in nature since, as set forth therein, static electricity had a tendency of discharging over the surface of the film thereby producing marks which ruin the film for projection purposes.

The art of mass spectrometry as set forth in the Craig and Schroeder patents, and the art of nonstatic photographic film as set forth in the Pitman, Seel, and Goberly patents, are incorporated herein by reference.

SUMMARY OF THE INVENTION It is an object of this invention to provide new and improved mass spectrometers and display members therefor which reduce the amount of fogging which tends to occur on the display members.

Another object of this invention resides in utilizing an electrically conductive photographic plate in combination with a mass spectrometer.

Still another object of this invention is to provide a new and improved mass spectrometer using an electrical- 1y conductive display member in an electrical circuit to remove any electrical charge which tends to build up on or about the photographic plate.

With these and other objects in view, the present invention contemplates a new and improved mass, spectrometer including means for producing a source of ions, a display member and means for deflecting ions from the source onto the member wherein the improvement resides in having a display member which comprises a substrate, an electrically conductive film on the substrate and a coating of material sensitive to ions deposited on the subtrate. In accordance with one embodiment of the invention, the display member includes a transparent substrate, an electrically conductive film on the substrate, and a coating of material sensitive to ions deposited on the substrate.

In a'specific embodiment of the invention, an improved mass spectrometer is described which includes means for producing a source of ions, a display member and means for deflecting ions from the source onto the display member whereby the improvement resides in having the display member comprise a transparent substrate, a thin optically transparent, electrically conductive film on the substrate, and a coating of photosensitive emulsion sensitive to ions deposited on the substrate. The mass spectrometer can further include means for coupling the conductive film of the display member to a potential source.

The amount of fogging is significantly reduced, due to reflected ions, by making the entire photoplate sufficiently conductive to dissipate the charge to ground as it is deposited. This is accomplished by depositing a conductive film on the glass substrate prior to coating it with photoemulsion so that it is between the glass and the emulsion. This permits charges to be dissipated much more rapidly. Suitable materials include, but are not necessarily limited to, gold, platinum, silver, titanium, Nichrome, and aluminum. These materials, preferably, are deposited in very uniform films 100 angstroms or less thick so that the transmission of the photoplate is not excessively reduced. Such depositions can be by known techniques, such as by sputtering, by electron beam, by evaporation, or by electroless deposition.

Other ways of making the photoplates conductive are to use conductive glass, semiconductor oxide film coatings such as tin oxide, and putting thin wires at the glass surface.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects, advantages and features of the present invention will appear upon consideration of the following detailed description of specific embodiments, in conjunction with the accompanying drawings, wherein:

FIG. 1 is a generally schematic view in section of the magnetic analyzer of a mass spectrometer including an ion collecting apparatus having an electrically conductive display member embodying the invention; and

FIG. 2. is a sectional view of a magnetic analyzer illustrated in FIG. 1 taken along the line 22 thereof.

DETAILED DESCRIPTION With reference to FIGS. 1 and 2, the magnetic analyzer comprises two magnetic poles 11-12 defining a gap 13 across which is formed the magnetic field and through which the beam of ions 14 from an ion source 16 is adapted to pass. The poles 1112 and the gap 13, together with coupling base member 15, form a magnetic circuit.

The display member comprises a glass plate 17 supported on insulating supports 1818 and having one surface coated with a transparent conductive film 19. The transparent conductive film 19 is coated with a layer 21 of material which is sensitive to ions. The layer 21 may be made of a photosensitive material, for example. The electrically conductive film 19 is coupled by suitable means as by a lead 22 to a source of potential 23. The source of potential 23 can be a reference source such as ground, or can be a variable voltage source which can be adjusted depending upon the sensitivity desired.

Preferably, it is desired to utilize a transparent substrate which is rendered electrically conductive, having a photosensitive emulsion thereon, in combination with the mass spectrometer. In this way, a developed transparent photographic plate can be accurately analyzed by suitable equipment such as an optical densitometer, since the state of the optical densitometry art is relatively advanced.

As a method of providing improved mass spectrographs, an ion source 16 is provided in accordance with known techniques. The ions from the source 16 are directed in a beam 14 to an electrically conductive photographic member. The conductive photographic member is coupled to a point of reference potential (which may be fixed or variable) to reduce fogging due to reflected ions. The photographic member is subsequently developed in the usual manner.

Other apparatus can be provided in accordance with the teachings of this invention. For example, the ions from an ion source can be directed onto an electrically conductive display member such as an aluminized luminescent screen, which luminescent screen serves to activate a mosaic of a television iconoscope pickup tube for subsequent conversion to suitable electrical signals. The aluminum coating can be coupled to a point of reference potential to reduce fogging due to reflected ions.

Various modifications will suggest themselves to those ordinarily skilled in the art in the light of applicants teaching herein. Therefore, it is desired that this invention be limited solely by the scope of the allowed claims.

What is claimed is:

1. In an improved mass spectrometry system which includes means for producing a beam of ions, means for accelerating the ions along a path, means for separating the accelerated ions according to mass, and a display member positioned to receive an impingement of the separated, accelerated ions, wherein the improvement resides in the display member which comprises:

a transparent substrate;

a layer of electrically conductive, optically transparent material on one surface of the substrate;

a layer of photosensitive material characterized by the ability to respond to ion impingement and produce a latent ionic image which may be subsequently developed into a fixed image, said layer of photosensitive material overlying the exposed surface of the electrically conductive, optically transparent material for receiving the accelerated ions to produce (1) References Cited latent ionic images and (2) charges of a polarity UNITED STATES PATENTS which normally oppose and disperse the impinging ions to fog the latent ionic images; and 2,748,288 5/1956 Saulmer 25065 means connected to said electrically conductive layer 5 3'118786 1/1964 Katchman et 250-55 X for dissipating the charges produced by the imping- OTHER REFERENCES ing ions Lo maintain a sharp delineation along the Ion Beam Electrography y R J McClure from edges oft elatent ionic images. 2- In a mass spectrometry System as defined in claim 1, The Review of Sc1ent1fic Instruments, v01. 36, N0. 8,

wherein the layer of photosensitive material is a silver 10 Augustl96spp'1246and1247' hahdemmure- WILLIAM F. LINDQUIST, Primary Examiner 3. In a mass spectrometry system as defined in claim 1, wherein the layer of conductive material is a metal of a U3, CL X R thickness less than 100 angstroms. 25049.5, 65 

